1. Field of the Invention
The present invention is directed to a process for guiding a strand in a continuous casting plant with a soft reduction zone in which hydraulic servo units continuously adjust the gap between oppositely located strand guide rollers, and to the corresponding strand guide for performing this process.
2. Description of the Prior Art
Continuous casting plants, especially continuous casting plants for steel, use rollers to guide the strand; these rollers limit the thickness of the strand which is not yet completely solidified and prevent bulging of the strand shell due to ferrostatic internal pressure.
Usually, groups of at least 4 pairs of rollers are combined in guide matter segments. The strand guide rollers arranged above the strand are fastened to a movable upper part, of the segment, while the strand guide rollers located below the strand are arranged at a fixed lower part, of the segment. The fixed part and movable part of the individual segment are connected with one another via 4 tension cylinders. These clamping cylinders, as they are called, pull the movable top part of the segment on spacers, so that the desired gap width results between the oppositely located rollers. This gap width of a segment of this type corresponds to the strand thickness.
A strand guide of the type mentioned above is known from DE 40 22 871 C2, wherein frame parts which carry the strand guide rollers that are located opposite to one another can be clamped relative to one another by means of a displacement device on one part of the segment until support devices contact counter-support devices which are provided with supporting surfaces located at different height positions and with counter-supporting surfaces, on the other part of the segment. The individual support disks are adjustable by means of rotation.
A device of this kind can only adjust a fixed gap width which cannot be readjusted during casting.
However, modern process technologies for improving product quality require that the gap width for a segment is changed during the casting process. In particular, soft reduction in the region of the lowest point of the liquid pool requires a wedge-shaped adjustment of the strand and a variable change in gap width of the corresponding segment.
A simple possibility for changing the gap width of segments with 4 clamping cylinders can be achieved in that the cylinders are constructed with position regulation as servo-hydraulic axles. In a solution of this type, the spacers, as they are called, can be dispensed with. The gap width of the segment is predetermined by a corresponding preset reference value for the 4 position-regulated piston-cylinder units. In so doing, the two servo units at the run-in end of the segment and the two servo units at the run-out end of the segment are regulated so as to be synchronized. Due to the use of a total of 4 servo units, this system is statically redundant.
DE 41 38 740 A1 discloses a process for the continuous casting of slabs or ingots in a continuous casting plant with a soft reduction zone which has rollers which can be continuously adjusted individually or as segments relative to one another by means of hydraulic cylinders and, with respect to their gap width, by means of spindles. The spindles can be moved to a desired gap spacing such that load is reduced. The movable part of the segment which is held in its position by four hydraulic cylinders is also statically redundant.